1. Field of the Invention
The present invention relates to an data storage system, and more particularly, to system and method for writing/reading data.
2. Background of the Related Art
In general, in the ferroelectric thin film memory, there are FRAM {Ferroelectric(non-volatile) Random Access Memory} of one transistor/one capacitor type as shown in FIG. 1 and Fe-FET(Ferroelectric Field-Effect Transistor) having a ferroelectric layer on a gate region as shown in FIG. 2. Recently, as the former has a structure and peripheral circuits similar to a DRAM (Dynamic Random Access Memory), many semiconductor production companies pay attention to the FRAM. It is recent trend that Ramtron of the USA or ROHM of Japan disclose fabrication of 64K FRAM and large sized DRAM companies are absorbed in researches and developments of 1M or 4M FRAM. However, being of a DRO(Destructive readout) type, the FRAM structure shows fatigue of the ferroelectric capacitor(spontaneous polarization is reduced as cycling is repeated) and has difficulty in high density packing of the devices as two transistors/two capacitors are used in a cell for improving a device reliability. Since a current device packing density of the DRAM is around 256 DRAM, it seems difficult that a device packing density of the FRAM is elevated to a high level within a short time. On the other hand, the Fe-FET type has difficulty in putting into practical use due to difficulty in realization, despite of its advantage of being an NDRO(Non-destructive readout) type drive. The difficulty comes from various problems, such as difficulty in injecting charges to an interface of a semiconductor of Si and a ferroelectric substance as the semiconductor and the ferroelectric substance should be bonded, directly. The recent development of scanning probe microscopy leads to a significant development of a technology for observing a structure of a size below 100 .ANG., to level at which even an atom(of a size below 2 .ANG.) can be detected in a high vacuum. If a ferroelectric domain(a size of domain may be around a few hundred .ANG. even though it is dependent on thermodynamic conditions) can be put under control and up/down of the domain can be detected, it can be expected that a data storage with a high device packing density each with very small scale (approx. over 100 Gbit/in.sup.2) can be realized. However, because the related art ferroelectric non-volatile memory has a limitation in high density writing and reading of data in view of its structure, there have been many difficulties in integrating the ferroelectric non-volatile memory.